1. Filed of the Invention
The present invention relates to an apparatus for conveying a circuit substrate such as a printed circuit board, and particularly to the improvement of an apparatus for conveying a circuit substrate on a belt or belts.
2. Related Art Statement
As a circuit substrate conveying apparatus of this kind, there is known an apparatus including two belts and two substrate guides. The two belts are provided at respective positions apart from each other in a first direction, include respective substantially horizontal, flat portions extending parallel to each other in a second direction perpendicular to the first direction, and are circulated such that the two flat portions are moved at the same speed in the same direction. One of the two substrate guides extends over one of opposite side portions of the flat portion of a corresponding one of the two belts, and the other substrate guide extends over one of opposite side portions of the flat portion of the other belt, such that the one side portion of the flat portion of the one belt is remoter from the other belt than the other side portion of the flat portion of the one belt in the first direction, and the one side portion of the flat portion of the other belt is remoter from the one belt than the other side portion of the flat portion of the other belt in the first direction. The two substrate guides have respective guide surfaces opposite to each other. The respective other side portions of the respective flat portions of the two belts provide respective substrate-convey portions which support opposite end portions of a circuit substrate and which convey the circuit substrate while opposite end surfaces of the circuit substrate are guided by the respective guide surfaces of the two substrate guides.
Generally, electric components (e.g., electronic components) are not mounted on portions of the circuit substrate which are supported by the respective substrate-convey portions of the two belts. Therefore, it is preferable to decrease the area of the portions of the circuit substrate which are supported by the respective substrate-convey portions of the two belts. For example, two belts each of which has a small width may be employed. In this case, even if the circuit substrate is supported by the respective entire widths of the two narrow belts, the portions of the circuit substrate supported by the belts are small. Accordingly, the electric components are mounted on the remaining large portions of the circuit substrate. However, since each of the two narrow belts is needed to have a great thickness to maintain the strength of the each belt, it is difficult to circulate the each belt at a small radius of curvature. Therefore, it is not easy to provide the conveying apparatus with desirable belts. On the other hand, two belts each of which has a great width and a small thickness may be employed. In the latter case, in addition to the two wide and thin belts, it is possible to provide two substrate guides one of which extends over one of opposite side portions of a flat portion of a corresponding one of the two belts, and the other of which extends over one of opposite side portions of the flat portion of the other belt, the one side portion of the flat portion of the one belt being remoter from the other belt than the other side portion of the flat portion of the one belt in the first direction, the one side portion of the flat portion of the other belt being remoter from the one belt than the other side portion of the flat portion of the other belt in the first direction. In this case, the area of portions of the two belts which can support the circuit substrate is decreased by the provision of the two substrate guides. Thus, the conveying apparatus can assure that circuit substrates are efficiently used and that the two belts have a sufficient strength and are easily provided. Additionally, the two substrate guides prevent the two belts from curving upward.
However, even if the two substrate guides are provided as mentioned above, a circuit substrate having a small thickness tends to enter a clearance which is left between each of the two substrate guides and a corresponding one of the two belts, whereby the conveying apparatus may not smoothly convey the circuit substrate. The each substrate guide and the corresponding belt are provided such that the clearance is as small as possible. Since some clearance is needed to allow the circulation of the each belt, it is impossible to prevent every sort of circuit substrate from entering the clearance, depending upon the thickness of the circuit substrate.